Fidel Castro has denounced the pending release in the US of a jailed Cuban militant who was once a US operative, accusing the American government of planning to free a "monster". Family members of alleged victims of Luis Posada Carriles joined a protest yesterday, saying that freeing him would be risky.

Posada, a former CIA operative, is wanted in Cuba in the 1976 bombing of a Cuban jetliner that killed 73 people, a charge Posada denies. Mr Castro has repeatedly accused the US government of protecting Posada by holding the 79-year-old on a far less serious charge.

Mr Castro's charges came in a signed letter distributed by foreign ministry officials after US district judge Kathleen Cardone refused to reverse her decision allowing Posada to be released on bail. "The answer is brutal," Mr Castro wrote. "The government of the US and its most representative institutions have decided the liberation of the monster beforehand."

The letter was the third in recent days signed by the ailing Cuban leader, who has not been seen in public for more than eight months. Mr Castro, 80, announced on July 31 he had undergone emergency intestinal surgery and provisionally ceded his presidential functions to his 75-year-old brother, Raul, the defence minister.

Fidel Castro's medical condition and ailment remain a state secret, but he is widely believed to suffer from diverticular disease, a common affliction among the elderly that causes inflammation and bleeding in the colon.

Ms Cardone ruled in El Paso, Texas, last Friday that Posada could be released on US$250,000 (£125,000) bond from the Otero County jail in New Mexico, pending trial on charges of lying to immigration authorities in a bid to become a naturalised citizen. Posada's family members in Miami must still post a $100,000 personal surety bond, said Arturo V Hernandez, Posada's lawyer in Miami.